The present invention relates to an improved catalytic process for isomerizing light paraffinic hydrocarbon feeds containing, calculated as sulfur, less than about 5 ppmw of sulfur-containing impurities.
It is well known in the art that in the typical production of motor fuel from crude oil in a refinery, a material portion of the product is a light paraffinic fraction (LPF). For example, in a refinery processing 50,000 barrels per day of crude oil, as much as 9000 barrels per day of LPF product may be produced. Typically, LPF product, although deficient in terms of octane-number quality, is added to the refinery gasoline pool. The octane number deficiency of the LPF component is usually made up by adding an octane improver to the pool, for example tetramethyl lead and/or a sufficient quantity of high-octane component, e.g., reformate. However, in the near future, in order to reduce environmental pollution, the amount of lead-containing compounds which may be added to gasoline will be severely limited by law. Consequently, there is a need for an effective process for upgrading LPF-type hydrocarbon mixtures. Normally, costly hydrogen gas is required for the isomerization reaction; our process, in contrast, provides for the in-situ generation of hydrogen gas. However, hydrogen generation by conventional reforming is normally effected under such severe conditions that excessive cracking of a portion of the feed to lighter hydrocarbon gases occurs. Accordingly, there is a need for generation of hydrogen gas in an isomerization process where loss of liquid feed to light gas production is minimal.
A two-stage process for catalytic reforming of a hydrocarbon charge containing less than 51 volume percent of cyclics is taught in U.S. Pat. No. 3,617,522. In the first stage, reforming of the charge is continued until the catalyst becomes relatively inactive. In the second stage, activity of the catalyst is restored and/or promoted by including water in the feed.
A process for isomerizing hydrocarbon feeds using a halided platinum-aluminum-rhenium catalyst is disclosed in U.S. Pat. Nos. 3,679,602 and 3,879,484.
A process for hydrotreating and isomerizing at relatively moderate temperatures C.sub.5 and C.sub.6 hydrocarbon streams is disclosed in U.S. Pat. No. 3,718,710.
A process for increasing yields in converting hydrocarbons by contact thereof with a platinum-alumina-rhenium catalyst in the presence of water vapor is taught in U.S. Pat. No. 3,816,300.
A method for maintaining the activity of a rhenium-containing catalyst at a high level is taught in U.S. Pat. No. 3,848,019 for use in isomerizing a hydrocarbon stream at temperatures in the range 100.degree. F. to 600.degree. F. In the method, a small amount of a halogen-containing compound is included in the feed.